The invention relates to a shaft bearing assembly, particularly for a miniature electric motor, comprising at least one bearing block made of a porous oil-impregnated material and formed with a bearing bore for receiving a shaft therein, and with an axial surface facing a thrust collar provided on said shaft.
Bearing assemblies of this type are commonly used in the field of miniature motor construction. The bearing blocks are generally made of sintered bronze and adapted to store a small oil supply sufficient for a hydrodynamic support of the shaft in the radial direction. The shaft is axially fixed by a thrust collar provided on the shaft, for instance, a thrust bearing disc mounted on the shaft so as to abut an end face of the bearing block. Usually, there are two bearing blocks provided at the opposite free ends of the shaft, the respective thrust collars permitting a certain axial play of the shaft. Although this play is indispensable for insuring low-friction rotation of the shaft, it permits the shaft to oscillate in the axial direction, resulting in the creation of undesirable noise, the axial oscillations causing the thrust collars to collide with the axial faces of the bearing blocks. If one considers that these miniature motors are employed in particularly noise-sensitive appliances, such as HiFi tape recorders or video recorders, it is evident that the reduction of the running noise of such a motor is of enormous importance.
It is therefore an object of the invention to reduce the noises resulting from axial displacements of the shaft in the shaft bearing assembly.
The object is attained according to the invention by the provision that between the thrust collar of the shaft and the axial surface of the bearing block there is provided an oil-impregnated dampening disc made of an absorbent material the capillary action of which is greater than that of the porous bearing block.
The absorbent material of the dampening disc acts as a cage for the oil contained in the material. The material of the dampening disc is thus in fact effective to captivate a drop of oil and to retain it in the gap between the axial face of the bearing block and the thrust collar. The thus persistent presence of the drop of oil is effective to dampen the axial oscillations of the shaft, resulting in an enormous reduction of the noises otherwise generated thereby. The fact that the capillary action of the material of the dampening disc is greater than that of the porous bearing block is effective to prevent the oil from the dampening disc to be sucked into the bearing block. Quite to the contrary, the greater capillary action of the dampening disc causes oil from the bearing block to be sucked into the dampening disc, so that the latter is always saturated with oil. Since no oil can escape from the dampening disc, an equilibrium is established between the oil husbandry of the dampening disc and that of the bearing block.
The distance between the bearing block and the thrust collar advantageously corresponds substantially to the thickness of the oil-impregnated dampening disc. The dampening disc may definitely be inserted with a certain play in the gap between the bearing block and the thrust collar. A suitable material for making the dampening disc may, for instance, be an oil-resistant fiber fleece. It has been found particularly suitable to use a synthetic leather material for making the dampening disc. This material inherently has a greater capillary action than the conventionally employed sintered bronze bearings, and is also sufficiently oil resistant.
An embodiment of the invention shall now be described by way of example with reference to the accompanying drawings, wherein.